A hypothetical reference decoder (HRD) is valuable in compressed video systems because it serves to validate an encoded bitstream for compliance to a standard. In a coding standard such as H.264/AVC, there are numerous interoperability points within the Multiview Video Coding (MVC) feature of the standard. MVC allows the decoder to decode one or more views simultaneously, and decoding of one view may need information from other views. The H.264/AVC standard has rules (also referred to as requirements, constraints, or operational specifications) defining an HRD. The HRD conformance is a normative part of the H.264/MPEG-4 AVC standard. Any AVC bitstream has to be compliant to the HRD built according to the rules. Currently, there is no rule defined for a MVC HRD. Previous HRDs do not have sufficient rules to allow them to validate bitstreams like those of the MVC in AVC.
In many cases, the bit-rate variations of compressed bitstream need to be smoothed using buffering mechanisms at the encoder and decoder. The sizes of the physical buffers are finite, and hence the encoder constrains the bit-rate variations to fit within the buffer limitations. Video coding standards do not mandate specific encoder or decoder buffering mechanisms, but they require encoders to control bit-rate fluctuations so that a hypothetical reference decoder (HRD) (or Virtual Buffer Verifier (VBV)) of a given buffer size would decode the video bit stream without suffering from buffer overflow or underflow.
The HRD is based on an idealized decoder model. The purpose of a HRD is to place basic buffering constraints on the variations in bit-rate over time in a coded stream. These constraints in turn enable higher layers to multiplex the stream and cost-effective decoders to decode it in real-time. In the following discussion, H.264/AVC will be used as an example. However, the invention can be extended to other video coding models or standards.